Method for manufacturing a display device

ABSTRACT

A device-forming region where a semiconductor device is formed is arranged on a substrate in the matrix of 2×2. A linear laser beam has a cross-section having a length longer than the width of the device-forming region. When the irradiation of the laser beam is performed, the region irradiated with the end portions of the linear laser beams overlapped with each other or brought into contact with each other, is made positioned outside the device-forming region.

This application is a continuation of U.S. Ser. No. 09/211,719, filedDec. 14, 1998, now U.S. Pat. No. 6,156,997, which is a continuation ofU.S. Ser. No. 08/650,285, filed May 20, 1996, which is now U.S. Pat. No.5,893,990.

BACKGROUND OF THE INVENTION

The present invention relates to a laser processing method and a laserprocessing apparatus, and particularly, to an improvement of athroughout in an optical annealing step with respect to the manufactureof an insulated gate type semiconductor device such as a thin-filmtransistor (TFT) which is formed on a substrate having a crystallinesilicon film of non-single crystal and other semi-conductor devices.

Particularly, the present invention relates to the manufacture of asemiconductor device which is formed or an insulating substrate made ofglass or the like and having a large area.

Recently, studies have been made of an insulated gate type semiconductordevice including a thin-film like active layer (also referred to asactive region) on an insulating substrate. Particularly, studies havebeen made earnestly of thin-film like gate transistors, so-calledthin-film transistors (TFT). These transistors are classified by thematerial and crystalline state of a used semiconductor into an amorphoussilicon TFT, a crystalline silicon TFT, and the like. The crystallinesilicon is not a single crystal but a non-single crystal. Accordingly,the general term for these transistors is a non-single crystal TFT.

In general, the mobility of an amorphous semiconductor is small, so thatit can not be used as a TFT which is required high sped operation.Further, since the mobility of a P-type amorphous silicon is extremelysmall, thereby being unable to manufacture a P-channel TFT (TFT of PMOS)so that it is impossible to form a complementary MOS circuit (CMOS) bycombining the P-channel TFT with an N-channel TFT (TFT of NMOS).

On the other hand, the crystalline semiconductor has a mobility largerthan that of the amorphous semiconductor, so that high speed operationcan be achieved. By the crystalline silicon, not only TFT of NMOS butalso TFT of PMOS can be obtained, so that it is possible to form a CMOScircuit. The

The crystalline silicon film of non-single crystal has been obtained by,thermally annealing an amorphous silicon film obtained by a vapor phasedeposition method for a long time at an appropriate temperature(normally more than 600° C.) or by irradiating it with the intense lightsuch as a laser beam (optical annealing).

However, in the case where a glass substrate which is cheap and rich inworkability, is used as an insulating substrate, it has been extremelydifficult to obtain the crystalline silicon having a sufficiently highmobility (so high that a CMOS circuit can be formed) by only the thermalannealing. This is because the above-mentioned glass substrate hasgenerally a low distortion point temperature (about 600° C.), so that itis impossible to increase the substrate temperature up to a temperaturerequired to form the crystalline silicon film having the sufficientlyhigh mobility.

On the other hand, in the case where the optical annealing is used tocrystallize a silicon film based on a glass substrate, it is possible togive a high energy to orally the silicon film without increasing thesubstrate temperature to a very high temperature. Thus, the opticalannealing technique is regarded as very effective for crystallizing thesilicon film based on the glass substrate.

At present, a high power pulse laser such as an excimer laser is mostpreferable as an optical source for the optical annealing. The maximumenergy of this laser is very large as compared with a continuous-wavelaser such as an argon ion laser, so that it has been possible toimprove the throughput by using a large spot of more than several cm².However, when a normally used square or rectangular beam is used, itmust be moved up and down and right and left to process one substratehaving a large area. Thus, there is a room for improvement from theviewpoint of the throughput.

Concerning this, much improvement has been obtained by transforming abeam into a liner beam to extend the length of the beam (largeness ofthe cross section of the linear beam in the longitudinal direction) overa substrate to be processed, and by moving this beam relatively to thesubstrate to scan. Here, the scanning means that irradiation of thelaser beam is performed while the linear laser beam is moved in the linewidth direction (direction orthogonal to the longitudinal direction ofthe cross section of the linear beam), and the irradiated regions areoverlapped with each other not to separate the irradiated regions. Also,in general, when the irradiation of the linear laser beam is performedfor a large area, the scanning paths are made parallel to each other.

Further, before the optical annealing, when the thermal annealing iscarried out, it is possible to form a silicon film having more superiorcrystallinity. With respect to the method of the thermal annealing, asdisclosed in Japanese Patent Unexamined Publication No. Hei. 6-244104,by using the effect that an element such as nickel, iron, cobalt,platinum, or palladium (hereinafter referred to as crystallizationcatallytic element or simply referred to as catalytic element)accelerates the crystallization of amorphous silicon, the crystallinesilicon film can be obtained by the thermal annealing at a lowertemperature for a shorter time than a normal case.

However, in the above irradiation of the linear laser, in relation tothe maximum energy thereof, the length of the linear laser beam(largeness of the cross section of the laser beam in the longitudinaldirection) has been limited to about 20 cm at best.

If the processing is performed by the linear laser beam having a lengthlonger than the limit, the energy density of the laser beam becomesinsufficient to, for example, crystallize the amorphous silicon film.Thus, when a substrate having a large area is used and laser processingis performed for a region longer than the length of a linear laser beam,it has been necessary to perform scanning of the laser beam up and downand left and right, that is, both in the line width direction and in thelongitudinal direction. FIG. 13(B) schematically shows scanning paths ofa conventional laser beam.

FIG. 13(A) is a sectional view of a linear laser beam, and FIG. 13(B) isa view showing a surface to be irradiated viewed from the above. Asshown in FIG. 13(A), an end portion 1 a of a linear laser beam 1 is notcompletely rectangular, and the energy density in this portion isdispersed.

As shown in FIG. 13(B), the scanning of the linear laser beam 1 isperformed along two scanning paths 2 and 3. For example, after thedownward scanning of the linear laser beam 1 is performed along the leftscanning path 2, the downward scanning is performed along the rightscanning path 3. At this time, it is necessary to perform scanning sothat the end portions 1 a of the linear laser beams 1 are overlappedwith each other. Then, it becomes a problem how to overlap the endportions 1 a of the linear laser beams 1. In FIG. 13(B), a region 4shown in a rectangle is a region where scanning is performed by theoverlapped end portions 1 a of the linear laser beams 1 the surface tobe irradiated.

However, in general, since it is difficult to control the energy densityat the end portion 1 a of the linear laser beam 1, semiconductor devicesformed in the region 4 and in the neighborhood thereof are of extremelyuneven characteristics as compared with devices formed in other region.Thus, the semiconductor material in the region 4 is not suitable forprocessing of semiconductor devices.

As a countermeasure to the above problem, by irradiation of a laser beamthrough a slit, the end portion in the longitudinal direction in whichthe control of energy density is difficult, is shielded to shape the endportion of the laser beam. FIG. 14(A) is a sectional view showing alinear laser bear shaped by the slit, and FIG. 14(B) is a schematic viewshowing scanning paths of the laser beam and is a view showing a surfaceto be irradiated viewed from the above.

As shown in FIG. 14(A), through the slit, an end portion 5 a of a laserbeam 5 is shaped into a rectangle, so that the distribution of theenergy density in the end portion 5 a becomes uniform than the linearlaser beam 1 shown in FIG. 13(A). As shown in FIG. 14(B), when theirradiation of the linear laser beam 5 is performed, for example, thefollowing scanning steps may be made: after the downward scanning of thelinear laser beam 5 is performed along a left scanning path 6, thedownward scanning is performed along a right scanning path 7. At thistime, the scanning is performed so that the end portions 5 a of thelinear laser beams 5 are overlapped with each other. However, since theend portion 5 a of the laser beam 5 is shaped into a rectangle, and theenergy density distribution is uniform, it is sufficient to overlap theend portions 5 a of the linear laser beam 5 with each other to theextent that the end portions 5 a are brought into contact with eachother, as shown by reference numeral 8. Thus, it is possible to reducethe region 8 where the ends 5 a are overlapped with each other.

However, even if the energy density in the end portion 5 a of the laserbeam 5 is controlled by using the slit, the semiconductor devices formedin the region 8 to be scanned with the overlapped end portions 5 a ofthe laser beam 5, are of remarkable uneven characteristics as comparedwith devices formed in other region.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a laser processingmethod and a laser processing apparatus that can eliminate theabove-described problems and can perform the steps of laser annealingfor a semiconductor film having a large area with high throughput.

Another object of the present invention is to provide a laser processingmethod and a laser processing apparatus for a semiconductor film havinga large area, which can prevent unevenness of characteristics among aplurality of semiconductor devices.

In order to solve the problems, according to a first aspect of theinvention, a laser processing method is characterized in that when asemiconductor film, a width of which is longer than a length of thecross-section of a laser beam, is scanned and irradiated with the laserbeam having the linear cross section to perform annealing, asemiconductor device is not formed in a region irradiated with endportions of the laser beams in a longitudinal direction thereof whichare overlapped with each other or brought into contact with each other.

According to a second aspect of the invention, a laser processing methodis characterized by comprising the steps of: repeatedly scanning andirradiating a semiconductor film on a substrate with a laser beam havinga linear cross section; wherein the semiconductor film on the substrateincludes a plurality of device regions separated from one another; andwherein the semiconductor film is scanned with the laser beam in such amanner that a region irradiated with end portions of the laser beams ina longitudinal direction thereof, which are overlapped with each other,is positioned outside the device regions.

According to a third aspect of the invention, a laser processing methodin which a semiconductor film on a substrate is scanned and irradiatedwith a laser beam having a linear cross section, a length of the crosssection of the linear laser beam being shorter than a largeness of adevice region of the semiconductor region, the method is characterizedby comprising the steps of cutting an end portion of the linear laserbeam in a longitudinal direction thereof by the irradiation of thelinear laser beam to the semiconductor film through a slit; laserprocessing one portion of the device region through scanning of thelinear laser beam to form a laser-processed portion; and laserprocessing a non-laser-processed portion in the device region with a newlinear laser beam passing through the slit in such a manner that an endof the laser beam in a longitudinal direction thereof with which thelaser-processed portion has been scanned, is brought into contact withan end of the new laser beam in a longitudinal direction thereof.

According to a fourth aspect of the invention, a laser processing methodin which a semiconductor film on a substrate is scanned and irradiatedwith a laser beam having a linear cross section, a length of the crosssection of the linear laser beam being shorter than a largeness of adevice region of the semiconductor region, the method is characterizedby comprising the steps of: laser processing one portion of the deviceregion by scanning and irradiating the semiconductor film with thelinear laser beam to form a laser-processed portion, an end portion ofthe linear laser beam in a longitudinal direction thereof being cutthrough a slit; and laser processing a non-laser-processed portion inthe device region with a new linear laser beam passing through the slitin such a manner that an end of the laser beam in a longitudinaldirection thereof with which the laser-processed portion has beenscanned, is overlapped with an end of the new laser beam in alongitudinal direction thereof by a range of 10 to 20 μm.

According to a fifth aspect of the invention, a laser processing methodin which a semiconductor film on a substrate is scanned and irradiatedwith a laser beam having a linear cross section, a length of the crosssection of the linear laser beam being shorter than a largeness of adevice region of the semiconductor region, the method is characterizedby comprising the steps of cutting an end portion of the linear laserbeam in a longitudinal direction thereof by the irradiation of thelinear laser beam to the semiconductor film through a slit; laserprocessing one portion of the device region through scanning of thelinear laser beam to form a laser-processed portion; and laserprocessing a non-laser-processed portion in the device region with a newlinear laser beam passing through the slit in such a manner that an endof the laser beam in a longitudinal direction thereof with which thelaser-processed portion has been scanned, is brought into contact withan end of the new laser beam in a longitudinal direction thereof,wherein a semiconductor device is not provided in a subsequent step at aposition where the end portions are brought into contact with eachother.

According to a sixth aspect of the invention, a laser processing methodin which a semiconductor film on a substrate is scanned and irradiatedwith a laser beam having a linear cross section, a length of the crosssection of the linear laser beam being shorter than a largeness of adevice region of the semiconductor region, the method is characterizedby comprising: laser processing one portion of the device region byscanning and irradiating the semiconductor film with the linear laserbeam to form a laser-processed portion, an end portion of the linearlaser beam in a longitudinal direction thereof being cut through a slit;and laser processing a non-laser-processed portion in the device regionwith a new linear laser beam passing through the slit in such a mannerthat an end of the laser beam in a longitudinal direction thereof withwhich the laser-processed portion has been scanned, is overlapped withan end of the new laser beam in a longitudinal direction thereof by arange of 10 to 20 μm, wherein a semiconductor device is not provided ina subsequent step at a position where the end portions are overlappedwith each other.

According to a seventh aspect of the invention, a laser processingmethod of any one of the first to sixth aspects is characterized in thatthe substrate constitutes a liquid crystal display.

According to the present invention, when a semiconductor film having awidth longer than a cross section of a laser beam is scanned andirradiated with the linear laser beam to perform annealing, asemiconductor device is not formed in a region irradiated with endportions 1 a, 5 a of the laser beams 1, 5, as shown in FIG. 12, whichare overlapped with each other.

In other words, laser irradiation is controlled in such a manner that aregion irradiated with end portions of the laser beams in thelongitudinal direction thereof which are overlapped with each other orbrought into contact with each other, is not positioned on a deviceregion of the semiconductor film (where a semiconductor device isprovided).

According to this method, even if a substrate becomes large and a regionto be irradiated becomes large, laser annealing can be performed with ahigh throughput, and variation of characteristics among semiconductordevices can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a construction view of a laser irradiation apparatus of afirst embodiment and is also a top view;

FIG. 2 is a sectional view taken along line 2—2 in FIG. 1;

FIG. 3 is a sectional view taken along line 3—3 in FIG. 1;

FIG. 4 is a construction view showing laser irradiating means 39;

FIG. 5 is a construction view showing a lens system;

FIG. 6 is a construction view of a lens system and is also a sectionalview along a light path in FIG. 5;

FIGS. 7(A) to 7(C) are explanatory views showing forming steps of acrystalline silicon film in a second embodiment;

FIGS. 8(A) to 8(E) are explanatory views of scanning paths of a laserbeam;

FIG. 9 is an explanatory view of division of a substrate;

FIGS. 10(A) to 10(D) are explanatory views showing forming steps of aTFT in a third embodiment;

FIGS. 11(A) to 11(C) are explanatory views showing forming steps of aTFT in a third embodiment;

FIGS. 12(A) to 12(C) are explanatory views of scanning paths of a laserbeam in a fifth embodiment;

FIGS. 13(A) and 13(B) are explanatory views showing the shape of aconventional laser beam and a scanning method; and

FIGS. 14(A) and 14(B) are explanatory views showing the shape of aconventional laser beam and a scanning method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described withreference to the accompanying drawings.

[First Embodiment]

FIGS. 1 to 3 are construction views showing a laser irradiationapparatus of the first embodiment, in which FIG. 1 is a top view, FIG. 2is a sectional view taken along dotted line 2—2 in FIG. 1, and FIG. 3 isa sectional view taken along dotted line 3—3 in FIG. 1. The laserirradiation apparatus of this embodiment is an apparatus ofmulti-chamber type, and also a single wafer processing apparatus thatcan process a plurality of substrates (test pieces) continuously one byone.

A plurality of substrates 10 to be processed are contained in acartridge 11, and the substrates together with the cartridge 11 arecarried into the apparatus.

A cartridge carry-in and carry-out chamber 17, a heating chamber 18, anda laser irradiation chamber 19 are respectively connected by gate valves14 to 16 to a substrate transport chamber 13 for transporting thesubstrates 10 in the apparatus.

The substrate transport chamber 13, the cartridge carry-in and carry-outchamber 17, the heating chamber 18, and the laser irradiation chamber 19can be kept airtight, upper portions of which are respectively connectedto gas supply systems 20 to 23 for supplying a gas, an inert gas and thelike, and lower portions of which are respectively connected to exhaustsystems 29 to 32 connected with vacuum pumps 25 to 28. By thisstructure, atmospheres, pressures and the like in the substratetransport chamber 13, the cartridge carry-in and carry-out chamber 17,the heating chamber 18, and the laser irradiation chamber 19 can becontrolled.

A robot arm 33 is provided in the substrate transport chamber 13, sothat the substrates 10 can be transported into the cartridge carry-inand carry-out chamber 17, the heating chamber 18, or the laserirradiation chamber 19 one by one. Further, an alignment mechanism 34 isprovided at the side of the gate valve, so that positioning of thesubstrate 10 and the robot arm 33 is carried out.

In the heating chamber 18, a plurality of substrates 10 can be containedon an elevator 35, and the substrates 10 are heated up to apredetermined temperature by heating means 36 formed of resistors andthe like.

Further, in the laser irradiation chamber 19, a stage 37 on which thesubstrates 10 are set, is provided. The stage 37 includes heating meansfor heating the substrates 10, is freely and horizontally moved in thetwo-dimensional direction in the paper surface of FIG. 1 by a guidemechanism, motor and the like not shown, and is freely rotated around anaxis orthogonal to the paper surface. Further, a quartz window 38 onwhich laser light emitted from the outside of the apparatus is madeincident, is provided on the upper surface of the laser irradiationchamber 19.

As shown in FIG. 2, laser irradiation means 39 is provided in theoutside of the apparatus, a mirror 40 is arranged on an optical path 41of the laser light of the laser irradiating means 39 in the emittingdirection, and the quartz window 38 of the laser irradiation chamber 19is provided on the optical path 41 bent by the mirror 40. The laserlight emitted from the laser irradiation means 39 is reflected by themirror 40, passes through the quartz window 38, and is made incident orthe substrate 10 arranged on the stage 37.

FIG. 4 is a schematic construction view showing the laser irradiationmeans 39. Total reflection mirrors 52 and 53 are arranged on an opticalpath 50 of an oscillator 51, which generates the laser light, in theemitting direction thereof. On the optical path 50 in the reflectiondirection of the total reflection mirror 53, an amplifier 54, anattenuation means 55 formed of a plurality of filters 55 a to 55 d, andan optical system 56 for shaping the laser light into a linear beam aresequentially arranged.

The attenuation means 55 is for adjusting the laser energy. The filters55 a to 55 d have a function to attenuate the energy of transmittedlight. Transmissivities of these filters are different from one another.In this embodiment, the transmissivities of the filters 55 a to 55 d arerespectively 96%, 92%, 85%, and 77%. These filters 55 a to 55 d areindependently taken into and out of the optical path 50 by driving meanssuch as an electromagnet or a motor not shown. By suitably combining thefilters 55 a to 55 d, a filter with transmissivity of 57 to 96% can beformed. For example, by combining the filter 55 a of transmissivity of96% and the light reduction filter 55 b of transmissivity of 92%, alight reduction filter of transmissivity of 88% can be obtained.

The filters 55 a to 55 d are made of quartz coated-with layers ofhafnium oxide and silicon dioxide alternatively laminated. Thetransmissivity of the light reduction filters 55 a to 55 d depends onthe number of coated layers. In this embodiment, although the number ofthe filters 55 a to 5 d of the attenuation means 55 is four, theinvention is not limited to this number, but the number, transmissivityand the like of the filters may be determined so that the laser energycan be suitably adjusted.

FIGS. 5 and 6 are construction views showing the optical system 56, andFIG. 6 corresponds to a sectional view along the optical path 50 in FIG.5. As shown in FIGS. 5 and 6, on the optical path 50, a cylindricalconcave lens 61, a cylindrical convex lens 62, fly eye lenses 63 and 64having axes orthogonal to each other, cylindrical convex lenses 65 and66, and a total reflection mirror 67 are arranged sequentially from theincident direction. A cylindrical lens 68 is arranged on an optical pathin the reflection direction of the total reflection mirror 67.

In the laser irradiation means 39 shown in FIG. 4, the laser lightoscillated by the oscillator 51 is reflected by the total reflectionmirrors 52 and 53, and made incident on the amplifier 54. In theamplifier 54, the laser light is amplified, reflected by the totalreflection mirrors 52 and 53 respectively, passes through theattenuation means 55, and reaches the optical system 56. As shown inFIGS. 5 and 6, the laser light passes through the cylindrical concavelens 61, the cylindrical convex lens 62, and the fly eye lenses 63 and64, so that the energy distribution of the laser light is changed factthe Gaussian distribution type to the rectangular distribution type.Further, the laser light passes through the cylindrical convex lenses 65and 66, reflected by the total reflection mirror 67, and collected bythe cylindrical lens 63, so that a linear beam image is made on focalsurface f. This linear beam image has its longitudinal directionvertical to the paper surface in FIG. 6.

The shape of the laser beam immediately before being made incident onthe optical system 56 is a rectangle of 3×2 cm². However, after thelaser beam passes through the optical system 56, the beam is shaped intoa thin and long linear beam with a length of 10 to 30 cm and a width ofabout 0.1 to 1 cm.

In the case where laser annealing is performed by using the laserirradiation apparatus shown in FIGS. 1 to 3, the gate valves 14 to 16are first closed, and the substrate transport chamber 13, the heatingchamber 18, and the laser irradiation chamber 19 are filled with anitrogen gas.

Next, the cartridge 11 containing a plurality of substrates 10 iscarried in the cartridge carry-in and carry-out chamber 17 from theoutside. In the cartridge carry-in and carry-out chamber 17, a door notshown is provided. By closing and opening this door, the cartridge 11 iscarried in and carried out. After the cartridge 11 is carried in thecartridge carry-in and carry-out chamber 17, the door is closed to sealthe cartridge carry-in and carry-out chamber 17, and the nitrogen gas issupplied from the gas supply system 21 to fill the cartridge carry-inand carry-out chamber 17 with the nitrogen gas. The pressure in thecartridge carry-in and carry-out chamber 17 is not specifically reduced,but kept at an atmospheric pressure. Next, the gate valve 14 and thegate valve 15 are opened. The gate valve 14 may be kept open until aseries of steps are ended.

By the robot arm 33, the substrates 10 are taken from the cartridge 11set in the cartridge carry-in and carry-out chamber 17 one by one, andare mounted on the alignment mechanism 34. After the robot arm 33 andthe substrate 10 are once positioned, the substrate 10 is again taken bythe robot arm 33, and transported into the heating chamber 18. At eachtime when the substrates 10 are transported into the hearing chamber 18,the elevator 35 rises or falls so that the substrates 10 are containedin the sequentially laminated state.

After a predetermined number of substrates 10 are transported into theheating chamber 18, the gate valve 15 is closed, and the substrates 10are heated by the heating means 36. When the substrates 10 are heated toa predetermined temperature, the gate valve 15 is opened, the substrates10 are transported to the substrate transport chamber 13 from theheating chamber 18 by the robot arm 33, set on the alignment mechanism34, and again positioned.

After the gate valve 16 is opened, the substrate 10 on the alignmentmechanism 34 is set on the stage 37 in the laser irradiation chamber 19by the robot arm 33, then the gate valve 15 and the gate valve 16 areclosed. It is preferable that the gate valve 15 is opened and closed ateach time when the transport of the substrate is performed. This isbecause it is preferable to prevent the atmosphere in the heatingchamber 18 from exerting thermal affection to the mechanical structuresuch as the robot arm 33.

After the gate valve 16 is closed, the linear laser beam is emitted fromthe laser irradiation means 39, and the linear laser beam is madeincident on the substrate 10 on the stage 37 through the mirror 40 andthe quartz window 38. The linear laser beam is made incident on thesubstrate 10 along the predetermined scanning path by rotating andhorizontally moving the stage 37. During the irradiation of the laserbeam, the substrate 10 is heated to the same temperature as atemperature in the heating chamber 18 by the heating means provided inthe stage 37, so that thermal variation is suppressed. When theirradiation of the laser beam is ended, the gate valve 16 is opened, andthe substrate 10 is contained in the cartridge 11 in the cartridgecarry-in and carry-out chamber 17 by the robot arm 33. In this way, theprocess for one substrate 10 is ended.

When the process for one substrate 10 is ended, the gate valve 15 isopened, the following substrate 10 is taken from the heating chamber 18by the robot arm 33, transported into the laser radiation chamber 19,set on the stage 37, and irradiated with the laser beam. In this way,the substrates 10 contained in the heating chamber 18 are irradiatedwith the laser beam one by one. When all steps are ended, all substrates10 to have been processed are contained in the cartridge 11 set in thecartridge carry-in and carry-out chamber 17. This cartridge 11 is takenfrom the cartridge chamber 17, and the process may proceed with a nextstep.

It is necessary that the heating temperature in the heating chamber 18is made lower than a temperature at which the amorphous silicon film iscrystallized. This is because time intervals in which the substrates 10are in the heating chamber, are different from each other. In general,the heating temperature in the heating chamber 18 is selected to beabout 200 to 400° C. Further, it is necessary that this heatingtemperature is made the same as a heating temperature of the substrate10 at the irradiation of the laser light.

[Second Embodiment]

In this embodiment, there is shown a case where a substrate having asize exceeding a linear laser beam is used, and the crystalline siliconfilm for manufacturing a semiconductor device is formed. FIGS. 7(A) to7(C) are views showing manufacturing steps of the crystalline siliconfilm.

As shown in FIG. 7(A), on a glass substrate 71 (in this embodiment,Corning 7059 of 360 mm×460 mm is used), a silicon oxide film as an underfilm 72 of a thickness of 2000 Å, and an amorphous silicon film 73 of athickness of 500 Å are continuously formed by a plasma CVD method.

Then, a nickel acetate solution of 10 ppm is coated on the surface ofthe amorphous silicon film 73 by a spin coat method, and the surface isdried to form a nickel layer 74. When a surface active agent was addedinto the nickel acetate solution, a better result was obtained. Sincethe nickel-layer 74 is very thin, it is not necessarily a film. However,there is no problem in the subsequent steps.

As shown in FIG. 7(B), the amorphous silicon film 73 is annealed at 550°C. for four hours to crystallize the amorphous silicon film, so that thecrystalline silicon film 75 is obtained. By heating, the nickel in thenickel layer 74 functions as nuclei of crystal, so that crystallizationof the amorphous silicon film 73 is accelerated. Thus, the crystallinesilicon film 75 can be obtained at a low temperature such as 550 ° C.(less than a distortion temperature of Corning 7059) and for a shorttime such as four hours.

It was preferable that the concentration of catalytic element in thecrystalline silicon film 75 was 1×10¹⁵ to 1×10¹⁹ atom/cm³. If theconcentration is less than 1×10¹⁵ atom/cm³, it is difficult to obtainthe catalytic effect to accelerate the crystallization. If theconcentration is higher than 1×10¹⁹ atom/cm³, metallic characteristicsappear in the silicon, so that semiconductive characteristics disappear.In this embodiment, the minimum value of the concentration of thecatalytic element in the crystalline silicon film 75 was 1×10¹⁷ to5×10¹⁸ atom/cm³. These values were analyzed and measured by a secondaryion mass spectroscopy (SIMS).

In order to further improve the crystallinity of the thus obtainedcrystalline silicon film 75, as shown in FIG. 7(C), the film 75 isirradiated with an excimer laser of a large power pulse laser to formthe crystalline silicon film 76 having superior crystalline properties.

When the irradiation of a laser beam is performed, using the apparatusas shown in FIGS. 1 to 6, a KrF excimer laser beam (wavelength 248 nm,pulse width 30 nsec) is shaped into a linear beam of 1 mm×185 mm, theirradiation of the laser beam with the energy density of about 220mJ/cm² is first performed, and then the irradiation of the laser beamwith the energy density within the range of 100 mJ/cm² to 500 mJ/cm²,for example, with the energy density of 370 mJ/cm² is performed. Also,when attention is paid to one point of a material to be irradiated, thescanning speed of the laser beam, actually the moving speed of the stage37 on which the substrate 71 is set, is adjusted so that he irradiationof 2 to 20 shots of the laser beam is performed.

The change of the laser energy from 220 mJ/cm² to 370 mJ/cm² is carriedout in such a manner that in the laser irradiation means 39 shown inFIG. 4, the filters 55 a to 55 d of the attenuation means 55 areselectively inserted into and retracted from the optical path 50 in thestate in which the output of the oscillator 51 is kept constant. Thesubstrate temperature at the laser irradiation is 200° C.

It is assumed that such an irradiating method with changed irradiationenergies is referred to as multi-stage irradiation. In this embodiment,irradiation is performed twice, so that two-stage irradiation isperformed. By the two-stage irradiation, the crystallinity of thecrystalline silicon film 76 can be further improved than one-stageirradiation. In case of the one-stage irradiation, the irradiation ofthe laser beam with the energy density within the range of 100 mJ/cm² to500 mJ/cm², for example, with the energy density of 370mJ/cm² may beperformed.

FIGS. 8(A) to 8(D) show scanning paths of the laser beam in thisembodiment. As shown in FIGS. 8(A) to 8(D), or the surface of thesubstrate 80 to be irradiated, rectangular device-formation regions 81on which thin-film transistors are formed, are arranged in the matrix of2×2. Thus, on the glass substrate 71 shown in FIG. 7(C), semiconductordevices are formed by using only the crystalline silicon 76 in thedevice-formation region 81. The substrate 80 on which semiconductordevices are formed, are divided into four device-substrates 86A to 86Das shown in FIG. 9.

Also, as shown in FIG. 9, it is presumed that after semiconductordevices are formed, the substrate 80 is divided into pieces having alength shorter than the length of the linear laser beam. Thus, in orderto achieve the state that the region 4 or 8 shown in FIG. 13(B) or14(B), which is irradiated with the overlapped end portions of the laserbeams in the longitudinal direction thereof, are positioned outside thedevice formation region 81, length L of the linear laser beam 82 in thelongitudinal direction is made longer than width W of thedevice-formation region 81.

In order to achieve the two-stage irradiation, as shown in FIGS. 8(A) to8(C), scanning paths 83A to 83C are set to be parallel and to draw onecontinuous line so that the device-formation regions 81 are twiceirradiated with the linear laser beam 82, when one-stage irradiation isperformed, as shown in FIG. 8(D), for example, the scanning path 85 maybe set. The scanning paths 83A to 83C, and 85 are made in uniformdirection for all device-formation regions 81 on the same substrate 80.

In order to make scanning of the linear laser beam 82 along the scanningpaths as shown in FIGS. 8(A) to 8(C) or 8(D), the irradiation of thelinear laser beam 82 may be performed while the linear laser beam ismoved along the direction substantially orthogonal to the longitudinaldirection of the beam and relatively to the surface 80 to be irradiated.Actually, the laser beam 82 is not moved but the stage 37 is rotated andmoved horizontally in the laser irradiation apparatus shown in FIGS. 1to 3, so that the substrate having the surface 80 to be irradiated ismoved and the scanning of the linear laser beam 82 along the scanningpath 83A, 83B, or 83C is performed.

In this embodiment, since the width W of the device-formation region 81is shorter than length L of the linear laser beam 82, thedevice-formation region 81 is not scanned with the end portion of thelinear laser beam 82. Accordingly, the film quality of the thus obtainedcrystalline silicon film 76 can be made uniform, so that thecharacteristics of semiconductor devices formed in the device-formationregions 81 can be made uniform. Further, since many substrates on whichsemiconductor devices having the same characteristics are formed, can beproduced by one step by processing the substrate 80 with a large area,the throughput can be improved.

[Third Embodiment]

In this embodiment, using the crystalline silicon film 76 obtained inthe second embodiment, steps of forming a thin-film transistor fordriving picture elements of a liquid crystal display device will bedescribed. FIGS. 10(A) to 10(D) and 11(A) to 11(C) show manufacturingsteps of the thin-film transistor of this embodiment.

As shown in FIG. 10(A), a silicon oxide film with a thickness of 3000 Åas an under film 102 is deposited by a plasma CVD method or a lowpressure thermal CVD method on a glass substrate 101, and a crystallinesilicon film 103 made of a crystallized amorphous silicon film inaccordance with the crystallization steps shown in the secondembodiment, is formed on the surface of the under film 102.

Next, as shown in FIG. 10(B), the crystalline silicon film 103 is etchedinto island-like portions, so that a plurality of active layers 104 areformed at predetermined positions in a device-formation region 100. Inthis embodiment, as shown in FIGS. 8(A) to 8(D) and 9, since an objectis to provide four device-substrates with the same characteristics bydividing the glass substrate 101 into four pieces, the rectangulardevice-formation regions 100 on which thin-film transistors are formed,are arranged on the glass substrate 101 in the matrix of 2×2. Aplurality of active layers 104 are formed at predetermined positions inthe device-formation region 100. Thus, when the crystalline silicon film103 is obtained, the end portion of the linear laser beam is made not topass through the inside of the device-formation region 100.

Next, a silicon oxide film 105 constituting a gate insulating film andhaving a thickness of 1000 to 1500 Å is formed by the plasma CVD method,and an aluminum film constituting a gate electrode 106 and having athickness of 5000 Å is deposited by a sputtering method. If scandium of0.2 weight % is mixed in the aluminum in advance, it is possible toprevent generation of hillock or whiskers in the subsequent heatingsteps.

Next, the surface of the aluminum film is subjected to anodic oxidation,so that fine anodic oxidation material not shown is formed into a verythin film. Next, a mask 107 of a resist is formed on the surface of thealuminum film. At this time, since the fine anodic oxidation materialnot shown is formed on the surface of the aluminum film, it is possibleto form the mask 107 of the resist brought into close contact. Then,using the mask 107 of the resist, the aluminum film is etched to formthe gate electrode 106.

As shown in FIG. 10(C), while the mask 107 of the resist remains, thegate electrode 106 is subjected to anodic oxidation to form porousanodic oxidation material 108 with a thickness of 4000 Å. At this time,since the mask 107 of the resist is brought into close contact with thesurface of the gate electrode 106, the porous anodic oxidation material108 is formed only on the side of the gate electrode 106.

Next, as shown in FIG. 10(D), after the mask 107 of the resist is peeledoff, the gate electrode 106 is again subjected to the anodic oxidationin an electrolytic solution to form fine anodic oxidation material 109with a thickness of 1000 Å.

The anodic oxidation materials can be changed by changing the solutionused. In the case where the porous anodic oxidation material 108 isformed, an acid solution including citric acid, oxalic acid, chromicacid, or sulfuric acid of 3 to 20% may be used. On the other hand, inthe case where the fine positive anodic oxidation material 109 isformed, an electrolytic solution made of an ethylene glycol solutionwhich includes tartaric acid, boric acid, or nitric acid of 3 to 10% andPH of which is adjusted to about 7, may be used.

As shown in FIG. 11(A), with the mask of the gate electrode 106, theporous anodic oxidation material 108 around the gate electrode, and thefine anodic oxidation material 109, the silicon oxide film 105 is etchedto form the gate insulating film 110.

As shown in FIG. 11(B), after the porous anodic oxidation material 108is removed, by an ion doping method, impurities are injected into theactive layer 104 with the mask of the gate electrode 106, the fineanodic oxidation material 109, and the gate insulating film 110. In thisembodiment, in order to form a P-channel TFT, phosphine (PH₃) is used asa doping gas, so that phosphorus ions are doped. At the doping,conditions such as a dose amount and acceleration voltage are controlledso that the gate insulating film 110 functions as a semi-transparentmask.

As a result of doping, the phosphorus ions in high concentration areinjected into regions not covered with the gate insulating film 110, sothat a source region 111 and a drain region 112 are formed. Thephosphorus ions in low concentration is injected into regions coveredwith only the gate insulating film 110, so that regions 113 and 114 withlow concentration impurity are formed. Since impurities are not injectedinto regions immediately under the gate electrode 106, a channel region115 is formed.

Since the region 113 and 114 with low concentration impurity function ashigh resistance regions, they contributes to reduction of anoff-current. Especially, the low concentration impurity region 113 atthe side of the drain region 112 is referred to as LDD. Further, bysufficiently increasing the thickness of the fine anodic oxidationmaterial 109, the region immediately under the fine anodic oxidationmaterial 109 is made into an offset region, so that the off-current canbe reduced further.

After the doping step, in the laser irradiation apparatus shown in FIGS.1 to 3, the laser annealing is performed, so that the doped phosphorusions are activated. The annealing conditions in this case are such thatthe energy density of the laser is within the range of 100 mJ/cm² to 350mJ/cm², for example, 160 mJ/cm², the irradiation of 20 to 40 shots ofthe linear laser beams is performed when attention is paid to anarbitrary point on the surface to be irradiated, and the substratetemperature is kept at 200° C. Since one-stage irradiation is performed,the scanning of the linear laser beam may be performed along thescanning path 85 shown in FIG. 8(D) At this time, the end portion of thelinear laser beam is made not to pass through the device-formationregion 100.

After the laser annealing, the thermal annealing may be performed. Inthis case, heating at a temperature of 450° C. and for two hours may beperformed.

As shown in FIG. 11(C), by the plasma CVD method, a silicon oxide filmwith a thickness of 5000 Å as an interlayer insulator 116, is formed. Asthe interlayer insulator 116, a single layer film of silicon nitridefilm, or a laminated film of silicon oxide film and silicon nitride filmmay be formed instead of the single layer film of silicon oxide film.Next, by a well-known etching method, the interlayer insulator 116 madeof the silicon oxide film is etched, so that contact holes arerespectively formed in the source region 111 and the drain region 112.

Next, an aluminum film with a thickness of 4000 Å is formed by asputtering method, which is patterned to form electrodes 117 and 118connected to the source region 111 and the drain region 112. A siliconnitride film as a passivation film 119 is formed, and a contact hole forelectrode 118 at the side of the drain region 112 is formed in thepassivation film 119. Next, an ITO film is formed and patterned so thata picture element electrode 120 is formed in the contact hole connectedto the electrode.

After the above-described steps, the TFT having the LDD structure isformed in the device-formation region 100 on the glass substrate 101.Lastly, the substrate 101 is divided For each device-formation region100 as shown in FIG. 9, so that four pieces of panels for the liquidcrystal display device can be obtained.

In this embodiment, manufacturing steps of N-channel thin-filmtransistor for driving picture elements of the liquid crystal displaydevice have been explained. However, a thin-film transistor constitutinga peripheral driving circuit and a thin-film transistor for drivingpicture elements may be formed in one device-formation region 100 at thesame time. In this case, the conductivity of the thin-film transistormay be controlled by using a well-known CMOS technique so that thethin-film transistor constituting the peripheral driving circuit becomesa complementary thin-film transistor composed of an N-channel thin filmtransistor and a P-channel thin-film transistor.

[Fourth Embodiment]

This embodiment relates to a scanning path of a laser beam in the casewhere a substrate is not divided. In this case, there is the possibilitythat the region 4 in which end portions of a linear laser beam areoverlapped with each other as shown in FIG. 13(B), or the region 8 wherethe end portions are brought into contact with each other as shown inFIG. 14(B), is arranged in the device-formation region. In this case,semiconductor devices are arranged so that the semiconductor devices donot extend over (is not positioned at, is not positioned near) theregion 4 or 8 shown in FIG. 13(B) or 14(B).

For example, in FIGS. 10(A) to 10(D), in order not to make the activelayer 104 of the thin-film transistor and the region 4 or 8 overlap witheach other, the length of the linear beam may be adjusted so that theend portion of the laser beam passes through a region 200 where theactive layer 104 is not formed.

Depending on the density of the semiconductor devices on the substrate,it is determined whether the portion (joint portion) irradiated with theoverlapped ends of the linear laser beams is made a portion like theregion 4 in FIG. 13 where the end portions of the laser beams areoverlapped to some extent, or a portion like the region 8 in FIG. 14where the end portions are brought into contact with each other.

If the interval between semiconductor devices is the order ofmillimeter, the shape of the end portion of the linear laser beam, thatis, the distribution of energy density at the end portion does notbecome a problem. Accordingly, as shown in FIG. 13(A), it is possible toperform the irradiation of the linear laser beam without shaping the endportion 1 a of the linear laser beam 1. However, if the interval betweensemiconductor devices is less than the order of millimeters it isnecessary to shape the linear laser beam by a slit to make the rectangleend portion as shown in FIG. 14(A), and further to make scanning so thatthe end portions of the linear laser beam is brought into contact witheach other as shown in FIG. 14(B).

Further, if the interval between the semiconductor devices becomes theorder of micron, even if the scanning of the linear laser beam isperformed as shown in FIG. 14(B), due to the limit of accuracy inalignment or the like in the process, there is a fear that a device isformed in the region 8 where the end portion 5 a of the laser beam 5passes. That is, it is difficult to form a device in a region where theend portion 5 a of the laser beam 5 does not pass.

In the case where as a semiconductor device, for example, a panel of aliquid crystal display is formed, the interval at which thin-filmtransistors as semiconductor devices formed on the substrate is about 10μm to 100 μm. Thus, in this case, using the slit, the end portion of thelinear laser beam in the longitudinal direction thereof is cut, and thescanning of the linear laser beam is performed so that the jointportions of the linear laser beam, that is, the end portions of the beamare brought into contact with each other. In this case, if the jointportions are brought into close contact with each other by the accuracyof about 10 to 20 μm, the accuracy is sufficient. It is possible to forma panel for a liquid crystal display without forming semiconductordevices on the joint portion.

[Fifth Embodiment]

As shown in FIGS. 8(A) to 8(D), in the second embodiment, thedevice-formation regions 80 are arranged on the substrate 80 in thematrix of 2×2. In order to make the device-formation regions irradiateduniformly with the laser beam, it is preferable to arrange thedevice-formation regions symmetrically with respect to the substrate.Thus, the regions are preferably arranged in the matrix of 2n×2n (n isnatural numbers more than one). In this embodiment, as shown in FIGS.12(A) and 12(B), by using a substrate with a larger area, thedevice-formation regions 91 of 4×4 are arranged on the substrate, sothat by one step, sixteen pieces of substrates on which semiconductordevices having the same characteristics can be obtained from the onesubstrate 90.

In order to perform the two-stage irradiation of the linear laser beam92, for example, as shown in FIGS. 12(A) and 12(B), the scanning paths93A and 93B may be set. Further, in order to perform uniform scanning ofthe linear laser beam 93, the length L of the linear laser beam 92 inthe longitudinal direction thereof is made longer than the width W ofthe device-formation region 91, and the region irradiated with theoverlapped end portions of the laser beam 92 in the longitudinaldirection thereof is made the outside of the device-formation region 91.

As described above, according to the present invention, it is possibleto perform the step of laser annealing for a semiconductor materialhaving a large area with a high throughput. Further, according to thepresent invention, it is possible to suppress variation incharacteristics among a plurality of semiconductor devices formed by thelaser annealing process for a semiconductor film with a large area.

The present invention is specifically effective in the case where manyTFTs are formed on the glass substrate with a large area over the widthof the linear laser beam. Especially, when the substrate is forconstructing a liquid crystal display, it is expected that a largepicture surface is required, and the present invention can make such alarge surface. Thus, the present invention is useful in technology.

What is claimed is:
 1. A method for manufacturing a display devicecomprising the steps of: preparing a substrate having a first edge and asecond edge substantially perpendicular to each other; forming asemiconductor film over said substrate; scanning a first pulsed laserbeam over said semiconductor film in a first scanning direction alongsaid second edge of said substrate so as to irradiate a first region ofsaid semiconductor film, wherein one point of said first region of saidsemiconductor film is irradiated with at least two shots of said firstpulsed laser beam; subsequently scanning a second pulsed laser beam oversaid semiconductor film in a second scanning direction along said secondedge of said substrate so as to irradiate a second region of saidsemiconductor film, wherein one point of said second region of saidsemiconductor film is irradiated with at least two shots of said secondpulsed laser beam, wherein each of said first and said second pulsedlaser beams has a linear shape at a surface of said semiconductor filmalong said first edge of said substrate, and wherein said second regionand said first region have a portion overlapping with each other; andetching said semiconductor film irradiated by said first and said secondpulsed laser beams into a plurality of semiconductor layers to formtransistors in areas outside said portion.
 2. The method according toclaim 1 wherein said first and said second pulsed laser beams have alength of about 10 cm or more along said first edge on saidsemiconductor film.
 3. The method according to claim 1 wherein each ofsaid first and said second pulsed laser beams is produced from anexcimer laser.
 4. The method according to claim 1 wherein said scanningof said first pulsed laser beam and said scanning of said second pulsedlaser beam are performed by moving said substrate.
 5. The methodaccording to claim 1 wherein said first scanning direction is oppositeto said second scanning direction.
 6. The method according to claim 1wherein said display device is a liquid crystal display device.
 7. Amethod for manufacturing a display device comprising the steps of:preparing a substrate having a first edge and a second edgeperpendicular to said first edge; forming a semiconductor film over saidsubstrate; first scanning said semiconductor film with a first pulsedlaser beam in a first scanning direction along said second edge of saidsubstrate, whereby a first region of said semiconductor film iscrystallizedm, and wherein one point of said first region of saidsemiconductor film is irradiated with at least two shots of said firstpulsed laser beam; second scanning said semiconductor film with a secondpulser laser beam in a second scanning direction along said second edgeof said substrate, whereby a second region of said semiconductor film iscrystallized, wherein one point of said second region of saidsemiconductor film is irradiated with at least two shots of said secondpulsed laser beam, wherein each of said first and said second pulsedlaser beams has a linear shape at a surface of said semiconductor filmalong said first edge of said substrate, and wherein said second regionand said first region have a portion overlapping with each other; andetching a crystallized semiconductor film into a plurality ofsemiconductor layers for transistors so as to exclude said portion. 8.The method according to claim 7 wherein said first and said secondpulsed laser beams have a length of 10 cm or more along said first edge.9. The method according to claim 7 wherein each of said first and saidsecond pulsed laser beams is produced from an excimer laser.
 10. Themethod according to claim 7 wherein said first scanning and said secondscanning are performed by moving said substrate.
 11. The methodaccording to claim 7 wherein said first scanning direction is oppositeto said second scanning direction.
 12. The method according to claim 7wherein said display device is a liquid crystal display device.
 13. Amethod for manufacturing a display device comprising the steps of:preparing a substrate having a first edge and a second edgeperpendicular to said first edge; forming a semiconductor film over saidsubstrate; first scanning said semiconductor film with a first pulsedlaser beam by moving said substrate in a first scanning direction alongsaid second edge of said substrate, whereby a first region of saidsemiconductor film is irradiated with said first pulsed laser beam, andwherein one point of said first region of said semiconductor film isirradiated with at least two shots of said first pulsed laser beam;second scanning said semiconductor film with a second pulsed laser beamby moving said substrate in a second scanning direction along saidsecond edge of said substrate, whereby a second region of saidsemiconductor film is irradiated with said second pulsed laser beam,wherein one point of said second region of said semiconductor film isirradiated with at least two shots of said second pulsed laser beam,wherein each of said first and said second pulsed laser beams has alinear shape at a surface of said semiconductor film along said firstedge of said substrate, and wherein said second region and said firstregion have a portion overlapped with each other; and etching saidsemiconductor film irradiated with said first and said second pulsedlaser beams into a plurality of semiconductor layers for transistors soas to exclude said portion.
 14. The method according to claim 13 whereinsaid first scanning and said second scanning are performed tocrystallize said semiconductor film.
 15. The method according to claim13 wherein each of said first and said second pulsed laser beams isproduced from an excimer laser.
 16. The method according to claim 13wherein said first and said second pulsed laser beams have a length of10 cm or more along said first edge.
 17. The method according to claim13 wherein said first scanning direction is opposite to said secondscanning direction.
 18. The method according to claim 13 wherein saiddisplay device is a liquid crystal display device.
 19. A method formanufacturing a display device comprising the steps of: preparing asubstrate having a first edge and a second edge perpendicular to saidfirst edge; forming a semiconductor film over said substrate; firstscanning said semiconductor film with a first pulsed laser beam bymoving said substrate in a first scanning direction along said secondedge of said substrate, whereby a first region of said semiconductorfilm is crystallized, and wherein one point of said first region of saidsemiconductor film is irradiated with at least two shots of said firstpulsed laser beam; second scanning said semiconductor film with a secondpulsed laser beam by moving said substrate in a second scanningdirection along said second edge of said substrate, whereby a secondregion of said semiconductor film is crystallized, wherein one point ofsaid second region of said semiconductor film is irradiated with atleast two shots of said second pulsed laser beam, wherein each of saidfirst and said second pulsed laser beams has a linear shape at a surfaceof said semiconductor film along said first edge of said substrate, andwherein said second region and said first region have a portionoverlapped with each other; and etching a crystallized semiconductorfilm into a plurality of semiconductor layers for transistors so as toexclude said portion.
 20. The method according to claim 19 wherein saidfirst and said second pulsed laser beams have a length of 10 cm or morealong said first edge.
 21. The method according to claim 19 wherein eachof said first and said second pulsed laser beams is produced from anexcimer laser.
 22. The method according to claim 19 wherein said firstscanning direction is opposite to said second scanning direction. 23.The method according to claim 19 further comprising a step of forming adevice formation region in each of said first region and said secondregion by using at least one of said plurality of semiconductor layers.24. The method according to claim 19 wherein said display device is aliquid crystal display device.
 25. A method for manufacturing a displaydevice comprising the steps of: preparing a substrate having a firstregion and a second region adjacent to each other, said substrate havinga first edge and a second edge perpendicular to said first edge; forminga semiconductor film over said first and said second regions of saidsubstrate; first scanning a first portion of said semiconductor filmwith a first pulsed laser beam in a direction along said second edge ofsaid substrate, whereby said first portion of said semiconductor film isirradiated with said first pulsed laser beam, each of said first laserpulsed beam having a linear shape at a surface of said semiconductorfilm along said first edge of said substrate, wherein said first portionof said semiconductor film is located over said first region, andwherein one point of said first region of said semiconductor film isirradiated with at least two shots of said first pulsed laser beam;second scanning a second portion of said semiconductor film with asecond pulsed laser beam in said direction along said second edge ofsaid substrate, whereby said second portion of said semiconductor filmis irradiated with said second pulsed laser beam, each of said secondpulsed laser beam having a linear shape at said surface of saidsemiconductor film along said first edge of said substrate, wherein saidsecond portion of said semiconductor film is located over said secondregion, and wherein one point of said second region of saidsemiconductor film is irradiated with at least two shots of said secondpulsed laser beam; etching said semiconductor film after saidirradiation of said first and second pulsed laser beams to form a firstplurality of semiconductor layers over said first region of saidsubstrate and a second plurality of semiconductor layers over saidsecond region of said substrate; forming a first plurality of thin filmtransistors having said first plurality of semiconductor layers used asat least channel regions thereof over said first region of saidsubstrate; forming a second plurality of thin film transistors havingsaid second plurality of semiconductor layers used as at least channelregions thereof over said second region of said substrate; and dividingsaid substrate into at least first and second device-substrates so thatsaid first plurality of thin film transistors are located over saidfirst device-substrate and said second plurality of thin filmtransistors are located over said second device-substrate.
 26. Themethod according to claim 25 wherein said first and said second laserbeams have a length of 10 cm or more along said first edge.
 27. Themethod according to claim 25 wherein each of said first and said secondpulsed laser beams is produced from an excimer laser.
 28. The methodaccording to claim 25 wherein said first scanning and said secondscanning are performed by moving said substrate.
 29. The methodaccording to claim 25 wherein said device-substrate constitutes a panelfor said display device.
 30. The method according to claim 25 whereinsaid display device is a liquid crystal display device.
 31. A method formanufacturing a display device comprising the steps of: preparing asubstrate having a first edge and a second edge perpendicular to saidfirst edge; forming a semiconductor film over said substrate; firstscanning said semiconductor film with a first laser pulsed beam in afirst scanning direction along said second edge of said substrate,whereby a first region of said semiconductor film is irradiated withsaid first pulsed laser beam, and wherein one point of said first regionof said semiconductor film is irradiated with at least two shots of saidfirst pulsed laser beam; second scanning said semiconductor film with asecond pulsed laser beam in a second scanning direction along saidsecond edge of said substrate, whereby a second region of saidsemiconductor film is irradiated with said second pulsed laser beam,wherein one point of said second region of said semiconductor film isirradiated with at least two shots of said second pulsed laser beam,wherein each of said first and said second pulsed laser beams has alinear shape at a surface of said semiconductor film along said firstedge of said substrate; etching said semiconductor film of said firstregion and said second region into a plurality of semiconductor layers;forming a plurality of device formation regions in each of said firstregion and said second region by using at least one of said plurality ofsemiconductor layers; and dividing said substrate into a plurality ofdevice-substrates so that each of said plurality of device-substratescontains at least one of said plurality of device formation regions. 32.The method according to claim 31 wherein said first and said secondpulsed laser beams have a length of 10 cm or more along said first edge.33. The method according to claim 31 wherein each of said first and saidsecond pulsed laser beams is from an excimer laser.
 34. The methodaccording to claim 31 wherein said first scanning direction is oppositeto said second scanning direction.
 35. The method according to claim 31wherein said first scanning and said second scanning are performed tocrystallize said semiconductor film.
 36. The method according to claim31 wherein a plurality of thin film transistors for driving a pluralityof picture elements and for constituting a driver circuit are formed insaid device formation region.
 37. The method according to claim 31wherein said device-substrate constitutes a panel for said displaydevice.
 38. The method according to claim 31 wherein said display deviceis a liquid crystal display device.
 39. A method for manufacturing adisplay device comprising the steps of: preparing a substrate having afirst edge and a second edge perpendicular to said first edge; forming asemiconductor film over said substrate; first scanning saidsemiconductor film with a first pulsed laser beam in a first scanningdirection along said second edge of said substrate, whereby a firstregion of said semiconductor film is irradiated with said first pulsedlaser beam, and wherein one point of said first region of saidsemiconductor film is irradiated with at least two shots of said firstpulsed laser beam; second scanning said semiconductor film with a secondpulsed laser beam in a second scanning direction along said second edgeof said substrate, whereby a second region of said semiconductor film isirradiated with said second pulsed laser beam, wherein one point of saidsecond region of said semiconductor film is irradiated with at least twoshots of said second pulsed laser beam, wherein each of said first andsaid second pulsed laser beams has a linear shape at a surface of saidsemiconductor film along said first edge of said substrate, and whereinsaid second scanning direction is opposite to said first scanningdirection; etching said semiconductor film of said first region and saidsecond region into a plurality of semiconductor layers; and forming adevice formation region in each of said first region and said secondregion by using at least one of said plurality of semiconductor layers.40. The method according to claim 39 wherein said first and said secondpulsed laser beams have a length of 10 cm or more along said first edge.41. The method according to claim 39 wherein each of said first and saidsecond pulsed laser beams is produced from an excimer laser.
 42. Themethod according to claim 39 wherein said first scanning and said secondscanning are performed by moving said substrate.
 43. The methodaccording to claim 39 wherein a plurality of thin film transistors fordriving a plurality of picture elements and for constituting a drivercircuit are formed in said device formation region.
 44. The methodaccording to claim 39 wherein said display device is a liquid crystaldisplay device.